[PATCH] debug: add sysrq_always_enabled boot option

Most distributions enable sysrq support but set it to 0 by default.  Add a
sysrq_always_enabled boot option to always-enable sysrq keys.  Useful for
debugging - without having to modify the disribution's config files (which
might not be possible if the kernel is on a live CD, etc.).

Also, while at it, clean up the sysrq interfaces.

[bunk@stusta.de: make sysrq_always_enabled_setup() static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 60 insertions, 18 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index d8323b8893c3..ef69c75780bf 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1656,6 +1656,12 @@ and is between 256 and 4096 characters. It is defined in the file
         sym53c416=      [HW,SCSI]
                         See header of drivers/scsi/sym53c416.c.
 
+        sysrq_always_enabled
+                        [KNL]
+                        Ignore sysrq setting - this boot parameter will
+                        neutralize any effect of /proc/sys/kernel/sysrq.
+                        Useful for debugging.
+
         t128=           [HW,SCSI]
                         See header of drivers/scsi/t128.c.
 
diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 05810c8d20bc..13935235e066 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -41,7 +41,34 @@
 #include <asm/irq_regs.h>
 
 /* Whether we react on sysrq keys or just ignore them */
-int sysrq_enabled = 1;
+int __read_mostly __sysrq_enabled = 1;
+
+static int __read_mostly sysrq_always_enabled;
+
+int sysrq_on(void)
+{
+        return __sysrq_enabled || sysrq_always_enabled;
+}
+
+/*
+ * A value of 1 means 'all', other nonzero values are an op mask:
+ */
+static inline int sysrq_on_mask(int mask)
+{
+        return sysrq_always_enabled || __sysrq_enabled == 1 ||
+                                                (__sysrq_enabled & mask);
+}
+
+static int __init sysrq_always_enabled_setup(char *str)
+{
+        sysrq_always_enabled = 1;
+        printk(KERN_INFO "debug: sysrq always enabled.\n");
+
+        return 1;
+}
+
+__setup("sysrq_always_enabled", sysrq_always_enabled_setup);
+
 
 static void sysrq_handle_loglevel(int key, struct tty_struct *tty)
 {
@@ -379,8 +406,7 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
                  * Should we check for enabled operations (/proc/sysrq-trigger
                  * should not) and is the invoked operation enabled?
                  */
-                if (!check_mask || sysrq_enabled == 1 ||
-                    (sysrq_enabled & op_p->enable_mask)) {
+                if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
                         printk("%s\n", op_p->action_msg);
                         console_loglevel = orig_log_level;
                         op_p->handler(key, tty);
@@ -414,9 +440,8 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
  */
 void handle_sysrq(int key, struct tty_struct *tty)
 {
-        if (!sysrq_enabled)
-                return;
-        __handle_sysrq(key, tty, 1);
+        if (sysrq_on())
+                __handle_sysrq(key, tty, 1);
 }
 EXPORT_SYMBOL(handle_sysrq);
 
diff --git a/drivers/char/viocons.c b/drivers/char/viocons.c
index 6d2e314860df..0e0da443cbd5 100644
--- a/drivers/char/viocons.c
+++ b/drivers/char/viocons.c
@@ -61,10 +61,7 @@
 static DEFINE_SPINLOCK(consolelock);
 static DEFINE_SPINLOCK(consoleloglock);
 
-#ifdef CONFIG_MAGIC_SYSRQ
 static int vio_sysrq_pressed;
-extern int sysrq_enabled;
-#endif
 
 #define VIOCHAR_NUM_BUF         16
 
@@ -936,8 +933,10 @@ static void vioHandleData(struct HvLpEvent *event)
          */
         num_pushed = 0;
         for (index = 0; index < cevent->len; index++) {
-#ifdef CONFIG_MAGIC_SYSRQ
-                if (sysrq_enabled) {
+                /*
+                 * Will be optimized away if !CONFIG_MAGIC_SYSRQ:
+                 */
+                if (sysrq_on()) {
                         /* 0x0f is the ascii character for ^O */
                         if (cevent->data[index] == '\x0f') {
                                 vio_sysrq_pressed = 1;
@@ -956,7 +955,6 @@ static void vioHandleData(struct HvLpEvent *event)
                                 continue;
                         }
                 }
-#endif
                 /*
                  * The sysrq sequence isn't included in this check if
                  * sysrq is enabled and compiled into the kernel because
diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
index 9df8833670cb..98a1d8cfb73d 100644
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -37,23 +37,37 @@ struct sysrq_key_op {
 
 #ifdef CONFIG_MAGIC_SYSRQ
 
+extern int sysrq_on(void);
+
+/*
+ * Do not use this one directly:
+ */
+extern int __sysrq_enabled;
+
 /* Generic SysRq interface -- you may call it from any device driver, supplying
  * ASCII code of the key, pointer to registers and kbd/tty structs (if they
  * are available -- else NULL's).
  */
 
-void handle_sysrq(int, struct tty_struct *);
-void __handle_sysrq(int, struct tty_struct *, int check_mask);
-int register_sysrq_key(int, struct sysrq_key_op *);
-int unregister_sysrq_key(int, struct sysrq_key_op *);
+void handle_sysrq(int key, struct tty_struct *tty);
+void __handle_sysrq(int key, struct tty_struct *tty, int check_mask);
+int register_sysrq_key(int key, struct sysrq_key_op *op);
+int unregister_sysrq_key(int key, struct sysrq_key_op *op);
 struct sysrq_key_op *__sysrq_get_key_op(int key);
 
 #else
 
+static inline int sysrq_on(void)
+{
+        return 0;
+}
 static inline int __reterr(void)
 {
         return -EINVAL;
 }
+static inline void handle_sysrq(int key, struct tty_struct *tty)
+{
+}
 
 #define register_sysrq_key(ig,nore) __reterr()
 #define unregister_sysrq_key(ig,nore) __reterr()
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 130c5ec9ee0b..600b33358ded 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -65,7 +65,6 @@ extern int sysctl_overcommit_memory;
 extern int sysctl_overcommit_ratio;
 extern int sysctl_panic_on_oom;
 extern int max_threads;
-extern int sysrq_enabled;
 extern int core_uses_pid;
 extern int suid_dumpable;
 extern char core_pattern[];
@@ -543,7 +542,7 @@ static ctl_table kern_table[] = {
         {
                 .ctl_name       = KERN_SYSRQ,
                 .procname       = "sysrq",
-                .data           = &sysrq_enabled,
+                .data           = &__sysrq_enabled,
                 .maxlen         = sizeof (int),
                 .mode           = 0644,
                 .proc_handler   = &proc_dointvec,